The present invention relates to improvements in ophthalmic mountings for use with bifocal lenses.
Many attempts have heretofore been made to raise and lower eyeglass lenses before the eyes of a user so that two or more different focal fields of the lenses can be moved into and out of desired position of use. Japanese laid-open utility model publication No. 63-122321 discloses an ophthalmic mounting for bifocal lenses, which permits two focal fields of the lenses to be moved to the most comfortable position of use for near or distance vision. The conventional mounting includes a sleeve secured to each nose pad by a pin, and a sliding member secured to each eyeglass rim. The sliding member is in the form of a rectangular frame and has a slightly arcuate spring. When the sliding member is inserted into the sleeve, the spring is urged against the pin so as to allow the near vision field of the bifocal lenses may be raised and lowered as desired and retain their positions of adjustment during use. A problem with this conventional mounting is such that the eyeglass frames or rims can not smoothly be moved to desired position of use due to frictional force developed between the spring and the pin.
One approach to this problem is disclosed in U.S. Pat. No. 5,691,796 issued to Negishi. In the patent to Negishi, a pair of upper magnets and a pair of lower magnets are secured to the upper and lower ends of nose pads, respectively. The nose pads include respective elongated guide recesses or bores of a circular cross section. A pair of slides are secured to a corresponding pair of pad arms. The slides have a circular cross section so that they can smoothly be moved within the guide recesses. A pair of movable magnets are secured to the respective slides. For distance vision, the movable magnets are magnetically attached to the lower fixed magnets. For near vision, the movable magnets are magnetically attached to the upper fixed magnets. The nose pads, when secured to the pad arms, are oriented to diverge downward. The guide recesses also diverge downward. In other words, the distance between the upper end of the right nose pad and that of the left nose pad is different from the distance between the lower end of the right nose pad and that of the left nose pad. The distance between the pad arms is however constant since the pad arms are secured to the respective rims. In this design, when the frame is lifted up for near vision, the nose pads are laterally spread due to friction between the slides and the guides recesses. This friction causes downward movement of the nose pads and thus, retards upward movement of the frame. When the frame is lowered to change from near vision to distance vision, the nose pads are forced to move toward each other due to fiction between the slides and the guide recesses. This friction causes upward movement of the nose pads and thus, retards downward movement of the frame.
Accordingly, it is an object of the present invention to provide an ophthalmic mounting for bifocal lenses which allows two or more different focal fields of lenses to be smoothly moved into and out of desired position of use.